In British patent specification No. 2 093 511 A there is disclosed pile-driving apparatus comprising a drop hammer for imparting blows to a pile, and a winch for lifting the drop hammer between successive blows. The winch comprises a winch drive, a winch drum, clutch means for disengageably engaging the winch drive with the winch drum, and a rope connecting the drop hammer to the winch drum, the rope passing over a sheeve. Sensing means is provided for sensing the load applied by the rope to the sheeve, and the output of the load sensitive means is fed to an analysis device. The analysis device is able to detect the moment of impact of the drop hammer on the pile, and provides an output causing the clutch to engage and the drop hammer therefore to be lifted. The winch drum is provided with marks, and fixed detectors are provided which are able to detect the direction of rotation and the angular position of the drum. The output of the detectors is fed to the analysis device which then provides a further signal to disengage the clutch when the drop hammer has reached a certain height. In this manner automatic operation of the pile driving apparatus is achieved.
The location of the load sensing means on what appears to be the mountings of the sheeve would require expensive modification of existing pile-driving apparatus. Furthermore, the location of the load sensing means at this critical point of the pile-driving apparatus can lead to long and costly breakdowns. Also, as will be apparent from the waveforms illustrated in FIGS. 2 and 3 of that specification, and by the fact that both the degree and direction of rotation displacement of the winch drum need to be detected, the analysis device will, of necessity, have to be of a complex nature, able to perform complex analyses, and, because of its complexity, be prone to malfunction.
It is an object of the present invention to provide pile-driving apparatus having control means for facilitating automatic operation of the apparatus, which control means is effective, simple in construction and operation, inexpensive, and can readily be incorporated in existing pile-driving apparatus of the manually operated kind.